I am sorry if I am asking a silly question but I am attempting to get better by following some guides and tutorials. One thing that has been confusing me for quite a bit is there is a certain source that I cannot apply a track matte to. I will explain everything that I am doing as thoroughly as I can.

I am busy creating a 3d wall that is currently only made up of 2 sources.

The first source is made up of many rectangles that fade in at random times until they are fully white. I did this by making a line of rectangles that do this first, then expanded it vertically, and then expanded it further to fill the whole composition.

The second source only has text in it.

The problem is that I want to apply a track matte to the first source but there is no drop-down menu.

Look at the bottomo left of ur AE interface...there are 3 toggle on/off switches...they are responsible for the properties of each layer u see in the timeline. Click the one regarding the matte properties and there u go!

A track matte is always a layer above the layer it is assigend to. You are having a severe misunderstanding here. The option will become avialable as soon as you add a third layer on top. Rather than jumping off with tutorials showing stuff that you may not understand, perhaps read the help about som basics?! Just sayin'...

Ah I see what I did wrong now. I have tried some basic tutorials, however this one is a lot more complex than those. I'm working on trying to understand what they are doing in this one and have already learnt some very useful stuff but you are right. I still have a lot to learn. I will continue to work my way down the list of basic tutorials I have found. Thanks a lot for your help.